The present invention is directed to electronic packaging and, more particularly, is directed to a lead free solder composition for the assembly of passive components and organic substrates with conventional ceramic packages.
A chip carrier may be attached to a circuit board by a ball grid array (BGA) or column grid array (CGA) comprising solder alloys. Such solder alloys have typically comprised an eutectic alloy composition of Pb/Sn. The chip carrier is typically a ceramic substrate carrying semiconductor chips. The BGA consists of an array of solder balls which are soldered to connecting pads on both the circuit board and the substrate.
U.S. Pat. No. 6,333,563 (Jackson et al.), the disclosure of which is incorporated herein by reference, teaches an organic interposer attached to a ceramic module using a high modulus underfill material. The organic interposer is then joined to an organic board. This assembly increases the fatigue life of the BGA electrical interconnection. The assembly uses standard Pb/Sn solders well known in the art.
For various reasons, however, the Industry is moving to a lead free solder strategy for component assembly. Any lead free interconnect structure will need to accommodate the various solder joint hierarchy temperatures involved. This will include not only conventional chip join and ball grid array to card assembly, but also organic interposer and passive component assembly as well.
Another problem addressed by the present invention relates to cooling the circuit chips. A current thermal solution for cooling circuit chips is to solder a heat sink to the chip. The preferred solder is eutectic PbSn or some combination of Pb and Sn depending on the temperature requirements of the various module interconnect components. As the industry migrates to lead free solder, this soldered chip/heat sink interface is an important consideration in solder hierarchy structure because the heat sink is typically attached to the chip prior to second level module to card assembly.
Accordingly, it is a purpose of the present invention to provide a lead free solder hierarchy structure for electronic packaging that includes organic interposers.
It is another purpose of the present invention to provide a lead free solder hierarchy structure for electronic packaging that includes passive components such as capacitors and resistors.
It is another purpose of the present invention to provide a lead free solder solution for the attachment of a heat sink to the circuit chip.
These and other purposes of the present invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.